The invention relates to an apparatus for measuring can seams, by means of which the seam of a can positioned on a measuring table by way of the seam, the latter being sawn open radially in a segment-like manner at least two to three times on the circumference, can be monitored and measured by means of a video camera and a lighting device.
The sealing of cans is ensured by correct sealing of the seam by connecting the top to the body of the can. It is thus necessary to randomly sample filled cans from an ongoing production as random samples, and saw open the seam in a segment-like manner two to three times on the circumference and to monitor the interior dimensions of the seam.
In the filling of drinks into cans using high-performance can-filling equipment with, for example, from 22 to 28 filling stations, it is necessary for at least one can per station and shift to be randomly sampled for a seam recheck. In each case seven features are measured on the can seam, which is sawn open three times on the circumference, i.e., with 22 stations and three shifts and 7 features, 462 measurements are determined per shift. Automation of this monitoring operation would thus save a substantial amount of time and improve the economics.
Previously, with the aid of a prism or deflecting mirror projecting into the free, sawn-open segment of the can, it has been practice to align perpendicularly the optical path of the viewing lens with the seam surface of the can, moved manually into the respective measuring position, and for the seam cross section either to be projected purely optically onto a viewing screen, and measured directly there, or to be transmitted from a video camera to a monitor and measured by mouse control using a suitable computer program (SEAM PROJECTOR DP1 brochure from Manfred Kuhnke Optische Me.beta.-und Kontrollapparate, Berlin and VIDEO SEAM MONITOR VSM III brochure from KUHNKE Can & End Testing Equipment, Berlin).
The liquid contents of drink cans must be emptied before the cans can be sawn open. It is not possible to prevent any remaining liquid contents from running out from the saw cut during measurement and soiling the deflecting mirror or the prism and thus adversely influencing the measurement result.
The measurement results may be further adversely affected by extraneous light.
These two mentioned adverse effects present an obstacle to automation of the measuring operation.